I've been working on something similar at my own house so bear with me while I nerd out on drainage systems for a moment here.
That downspout extension from the house on the left's gutter system is discharging too close to the concrete foundation wall. That along with the apparent lack of slope out of the side yard is causing excess water to build up between the two houses. If you look just above the grass line you can see that the force of that water pushing on the wall is slowly eroding away the concrete. It could already be causing major cracks in the foundation or other water related damages. If not corrected you could see significant settling of the house or even an eventual collapse of that wall. I would be surprised if the house on the right is not experiencing similar problems. You should put in a french drain and/or buried corrugated pipes connected to the gutter downspouts to mitigate that problem.
Thank you for coming to my Ted Talk. I hope you and that bunny both have a nice day.